Polymer matrix composite pushrod

ABSTRACT

In one embodiment, the invention comprises a polymer matrix pushrod comprising a composite rod having an annular collar affixed over each end portion of the composite rod and an endcap affixed at each end. The composite rod comprises a thermosetting polymer matrix and reinforcing fibers within the polymer matrix.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.10/950,076, filed Sep. 24, 2004, now allowed.

BACKGROUND

This invention relates to composite pushrods and more specifically, topolymer matrix composite pushrods.

Overhead valve internal combustion engines typically employ a “valvetrain” which regulates the motion of valves used to control the flow ofcombustion and exhaust gases into and out of each engine cylinder. Amongthe numerous components of such valve trains are “pushrods” which serve,among other components, to convert rotating motion from the rotatingcamshaft of the engine into linear motion of the individual valves oneach cylinder. It has long been recognized that improvements to thevalve train can lead to significant improvements in overall engineperformance. More particularly, valve train components of increasedstiffness, reduced weight and/or improved vibration damping propertieshave been suggested as possible enhancements to lower engine noise,increase engine speed, increase engine power and improve fuelefficiency, particularly in high performance overhead valve engines.

Pushrods made using polymer matrix composite materials have beenproposed as alternatives to traditional metal pushrods. In order toprovide sufficient wear of the pushrod at its ends, separate endcapstypically of a harder material, such as a metal, were fitted at bothends.

Male endcaps have been used at the ends of polymer matrix pushrods toprevent failures of the composite rod. However, “brooming” of the endsof the composite rod or tube still could occur due to compression forceson the ends of the pushrods and splitting of the composite tube stillcould occur if a typical interference fit endcap pin were used.

Female endcaps, i.e., endcaps having a crown and a skirt that fits overthe ends of the polymer composite rod, have been proposed to preventbrooming of the ends of the composite rod. Such female endcaps musttypically be custom designed and fabricated for these applications. Thisis because most commercially available endcaps for various roddiameters, tip diameters, and tip designs are male rather than female.Also, adhesive bonds used to hold the female endcaps on the rod aretypically less reliable than interference fit.

SUMMARY

In one embodiment, the invention comprises a polymer matrix pushrodcomprising a composite rod having an annular collar affixed over eachend portion of the composite rod and an endcap affixed at each end. Thecomposite rod comprises a thermosetting polymer matrix and reinforcingfibers within the polymer matrix.

In one aspect of the above embodiment, the composite rod has asubstantially uniform diameter along its length and the annular collarsare affixed over the surfaces of the end portions of the composite rod.

In another aspect of the above embodiment, the annular collars areaffixed over the end portions wherein the diameters of the end portionsof the composite rod are such that the outside diameters of the annularcollar are substantially the same as the outside diameter of theremainder of the composite rod.

In another embodiment, the invention comprises a polymer matrix pushrodcomprising a composite rod comprising a thermosetting polymer matrix andreinforcing fibers within the polymer matrix, a sleeve affixed over theoutside surface of the composite rod, and an endcap affixed at each endof the composite rod.

In another embodiment, the invention comprises a polymer matrix pushrodcomprising a composite rod comprising a thermosetting polymer matrix andreinforcing fibers within the polymer matrix, annular collars areaffixed over the end portions of the composite rod wherein the outsidediameters of the annular collar are substantially the same as theoutside diameter of the remainder of the composite rod, a sleeve affixedover the outside surface of the composite rod, and an endcap affixed ateach end of the composite rod.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of another embodiment of apolymer matrix composite pushrod of the invention

FIG. 2 is a schematic cross-sectional view of another embodiment of apolymer matrix composite pushrod of the invention.

FIG. 3 is a schematic cross-sectional view of another embodiment of apolymer matrix composite pushrod of the invention.

FIG. 4 is a schematic cross-sectional view of another embodiment of apolymer matrix composite pushrod of the invention.

FIG. 5 is a schematic cross-sectional view of another embodiment of apolymer matrix composite pushrod of the invention.

DETAILED DESCRIPTION

“Composite” as used herein means a combination of at least polymermatrix and reinforcing fibers on a macroscopic scale.

“Thermosetting polymer” means a polymer that solidifies or crosslinksirreversibly when heated or irradiated.

“Rod” includes solid and tubular or hollow rods.

“Fiber” as used herein includes monofilaments, tows, and yarns.

“Substantially continuous fiber” means a fiber that has a length ofsubstantially the length of a composite rod.

One embodiment of a pushrod of the invention is shown in FIG. 1 incross-section. Pushrod 10 comprises a hollow composite rod 12 havingannular collars 14 over the outside surface near the ends of thecomposite rod or end portions 18 and endcaps 16 at the ends of thecomposite rod 12. The composite rod 12 comprises a thermosetting polymermatrix and reinforcing fibers. Endcaps 16 have a crown 17 and a shank 18depending therefrom and which fits inside the aperture 15 in the end ofthe composite rod 12. Such endcaps are also known as “male” endcaps.Endcaps 16 may be affixed to the ends of the composite rod byinterference fit, adhesive bonding, or a combination of both, to theends of the composite rod.

In the pushrod of the invention shown in FIG. 1, the outside diameter ofthe composite rod is substantially uniform over the length of the rod.Because the outside diameter of the rod is substantially uniform overits length, the annular collars 14 are external to the outsidecylindrical surface of the composite rod, and have a larger outsidediameter than that outside diameter of the composite rod. The annularcollars have tapered ends 13 that are nearest the ends of the compositerod 12.

Although not required, such tapered ends on the annular collars may beneeded to provide clearance between a rocker arm and the end of thepushrod. The annular collars may be affixed over the outside surface ofthe ends of the composite rod by interference fit or by using a suitablehigh strength adhesive, or a combination of both. The length of theannular collar when affixed to the end portions of the composite rodtypically extends beyond the depth of the aperture for the shank. In oneembodiment, the length of the annular collar extends beyond the depth ofthe aperture a length that is at least about the diameter of the shank.The annular collars on each end portion are typically two separatecomponents as compared with a sleeve, described below.

The annular collars used over the outside surface near the ends of thecomposite rods inhibit splitting or “brooming” of the composite rod atand/or near the rod's ends. The annular collars on the composite rodsnear its ends may also provide physical interference for a durable andreliable attachment of a male endcap. Such an interference fit of theendcaps would likely not be possible without an annular collar thatresists any outward forces on the composite rod during insertion of amale endcap. In turn, any outward force provided by the shank of themale endcap desirably also holds the annular collar in place.

Typically for the combination of composite rod, collar, and endcap toform a robust pushrod, the collar and endcap shank desirably fits aroundand within the composite rod within certain interference ranges.Typically, the collar should have a nominal interference of about 0.025mm and not more than about 0.051 mm, with an interference range of fromabout 0.0000 mm to about 0.051 mm and any number or range in between.This means that the inside diameter of the annular collar is, forexample, from about 0.0000 mm to about 0.051 mm smaller than the outsidediameter of the composite rod where the annular collar is to be placed.Typically, the annular collars have a thickness sufficient to provide arobust pushrod for the intended application. In one embodiment, thethickness of the annular collar is at least about 0.024 in (0.061 cm).

Typically, the shank of the endcap should have a nominal interference ofabout 0.051 mm and not more than 0.0762 mm, with an interference rangeof from about 0.025 mm to about 0.0762 mm and any number or range inbetween.

Typically, the thickness of the wall of the composite rod that isbetween the annular collar and endcap shank is an effective thickness toprevent failure of the pushrod due to splitting, brooming, or loss ofendcap or collar. Typically, this wall thickness is at least about 1 mm.

Useful annular collars include those made from metals, such as steel,stainless steel, hardened steel, aluminum, and titanium and metalalloys.

Useful composite rods for pushrods of the invention comprise athermosetting polymer matrix and reinforcing fibers that are within orare embedded or substantially embedded within the polymer matrix.Desirably, the reinforcing fibers are substantially continuous. Thesubstantially continuous reinforcing fibers are also desirablysubstantially unidirectional, that is, aligned substantially parallel tothe central axis of the rod. Useful composite rods used in the pushrodsof the invention have compression strength of at least 150 ksi (1030MPa). In another embodiment, the composite rods used in pushrods of theinvention have compression strength of at least about 250 ksi (1700MPa).

Useful thermosetting polymer matrices comprise thermosetting polymershaving a glass transition temperature (Tg) of at least about 300° F.(149° C.). In another embodiment, useful thermosetting polymer matricescomprise thermosetting polymers having a glass transition temperature(Tg) of at least about 400° F. (204° C.). Examples of such thermosettingpolymers include, but are not limited to, epoxy resins, cyanate-esters,bismaleimides, phenolics, polyimides, and combinations thereof. Aspecific example of a useful thermosetting polymer is a two-partthermosetting resin sold under the tradename “MATRIMID 5292A” and“MATRIMID 5292 B” bismaleimide resin and curative (available fromHuntsman Advanced Materials Americas, Inc, of Brewster, N.Y.) which hasTg of about 400° F. (204° C.).

Specific examples of fibers useful in the composite pushrods of theinvention include those fibers which comprise polycrystalline ceramics,for example, polycrystalline alumina; boron; silicon carbide; glass;high modulus graphite; graphite; and aromatic polyamides andcombinations of such fibers. Useful commercially available fibersinclude those having the trade designation “NEXTEL 610” ceramic oxidefibers, “NEXTEL 650” ceramic oxide fibers, and “NEXTEL 720” ceramicoxide fibers (available from 3M Company, St. Paul, Minn.); “KEVLAR”fibers (available from DuPont, Wilmington, Del.); and boron and SiCfibers (available from Specialty Materials Corporation, Lowell, Mass.).Desirably, the reinforcing fibers have a tensile modulus of at leastabout 55 msi (380 MPa).

Generally, the reinforcing fibers are present in the thermosettingmatrix at a volume fraction of at least 55%. In other embodiments, thereinforcing fibers are present in the thermosetting matrix at a volumefraction of not more than 70%. In other embodiments, the reinforcingfibers are present in the thermosetting matrix at a volume fraction in arange of from about 55% to about 70% and any volume percentage and anyrange in between 55% and 70%. In other embodiments, the reinforcingfibers are present in the thermosetting matrix at a volume fraction in arange of about 60% to about 65%, and any volume percentage and any rangein between 60% and 65%.

Typically, the endcaps for the pushrods of the invention are made frommaterials suitable for use in an engine. Desirably, the endcaps have aRockwell C hardness of 55 or greater. Examples of suitable materialsinclude metal alloys and metals, such as steel, stainless steel,hardened steel, and nitride-coated titanium; and ceramic materials. Theendcaps may be the same or different at each end of the composite rod.The endcaps may also have holes for the passage of lubricant or coolantsuch as engine oil.

FIG. 2 shows a pushrod 20 of the invention comprising a composite rod 22comprising polymer matrix and reinforcing fibers with annular collars 24affixed over the end portions 26 of the composite rod and endcaps 28 ateach of the ends of the composite rod. Endcaps 28 have a crown 27 and ashank 29 depending therefrom and which fits inside the aperture 25 inthe end of the composite rod 22. In this embodiment, the diameter of theend portions 26 of the composite rod 22 are such that when annularcollars are adapted to fit over the end portions, the outside diametersof the annular collars 24 are substantially the same as the outsidediameter of the remainder of the composite rod. Such a combination ofsmaller diameter end portions of the composite rod and annular collarsprovide “flush-fitted” annular collars. Such flush-fitted annularcollars provide any needed clearance between a rocker arm or lifters andthe end of the pushrod. The annular collars 24 may be affixed over thecomposite rod by means of interference fit, adhesive bonding, or acombination of both, to the smaller diameter end portions of thecomposite rod.

In another embodiment, the pushrod 30 of FIG. 3 comprises a compositerod 32 and endcaps 34 at the ends of the composite rod. The compositerod 32 comprises a thermosetting polymer matrix and reinforcing fibers.Endcaps 34 have a crown 37 and a shank 38 depending therefrom and whichfits inside the aperture 35 in the end of the composite rod 32. A metalsleeve 36 is affixed over the outside surface of substantially theentire length of the composite rod. The metal sleeve 36 inhibitssplitting or “brooming” of the composite rod at and/or near the rod'sends. The metal sleeve may also provide physical interference for adurable and reliable attachment of a male endcap and provide protectionof the composite rod in applications where the composite rod may rubagainst adjacent parts. The metal sleeve may be affixed over thecomposite rod by interference fit, adhesive bonding, or a combination ofboth.

The metal sleeve 36 may be comprised of metals, or metal alloys suitablefor use in engines at typical engine temperatures. The metal sleeve mayalso be over the entire length or over only a portion of the length. Themetal sleeve may also have a solid surface or may have discontinuitiesin its surface, for example, holes or slits.

In another embodiment, the pushrod 40 of FIG. 4 comprises a compositerod 42 and endcaps 44 at the ends of the rod, annular collars 46 affixedover the smaller diameter end portions 48 of the rod as in FIG. 2.Endcaps 44 have a crown 43 and a shank 45 depending therefrom and whichfits inside the aperture 47 in the end of the composite rod 42. A metalsleeve 49 is affixed over the outside surface of substantially theentire length of the composite rod and including the outside surface ofthe annular collars. The metal sleeve may also be over the entire lengthor over only a portion of the length. The metal sleeve may be affixedover the composite rod by interference fit, adhesive bonding, or acombination of both.

In another embodiment, the pushrod 50 of FIG. 5 comprises a compositerod 52 and endcaps 54 at the ends of the rod, annular collars 56 overthe smaller diameter end portions 58 of the composite rod as in FIG. 3.Endcaps 54 have a crown 53 and a shank 55 depending therefrom and whichfits inside the aperture 57 in the end of the composite rod 52. Anon-metallic sleeve 59 is affixed over the outside surface ofsubstantially the entire length of the composite rod 52. Although thenon-metallic sleeve is shown covering substantially the entire length,the non-metallic sleeve may also cover a portion or portions of theoutside surface or surfaces of the composite rod. In this embodiment,the non-metallic sleeve 59 comprises a polymeric material. Thenon-metallic sleeve provides abrasion and cut resistance for thecomposite rod. The non-metallic sleeve also provides protection to anyuser or handler of a machined composite rod from any splinters causedfrom fiber exposure.

Useful polymeric materials for non-metallic sleeves include those thatprovide cut and abrasion resistance, are solvent and lubricantresistant, and can withstand operating temperatures of at least about250° F. (121° C.), and in other embodiments, at least about 350° F. (177C). In another embodiment, the non-metallic sleeve comprises aheat-shrinkable polymer material. The non-metallic sleeves may beaffixed to the composite rod by interference fit, adhesive bonding, or acombination of both.

The polymer matrix composite materials used in the present invention aregenerally made by forming a prepreg of fibers and thermosetting polymerresin, winding the prepreg around a mandrel, and then consolidating theprepreg to form a composite rod.

To achieve a desired surface finish and outside dimensions, thecomposite rod may be subjected to machining steps using, for example, apolycrystalline diamond-tipped cutting tool on a lathe, or adiamond-impregnated grinding apparatus. The composite rod either mayhave a constant diameter or it may be tapered or shaped in a manner suchthat the rod is thicker or has a larger diameter in portions of the rod.Alternatively, a grinder can be used to machine the composite rod to adesired dimension with a desired surface finish. The composite rods areeach then cut to their desired length using, for example, adiamond-tipped cutter. The cut typically is a straight cut, madeperpendicular to the long (central) axis of the pushrod.

EXAMPLES Example 1

The prepreg material, which comprised 65% by volume alpha-alumina fiber(available under the trade designation “NEXTEL 610” from 3M Company;organic sized) and 35 percent by volume epoxy resin (obtained under thetrade designation “EPON 828” from Resolution Performance Products,Houston, Tex.), was made by Aldila Corp, Poway, Calif. The prepreg had10,000 denier tows of fiber spread at 10.42 tows per inch. A portion ofprepreg (6.172 in (15.68 cm)×11.5 in (29.21 cm)); (24.13 g) was used.

Knowing the density of the epoxy resin (1.21 g/cc) and the “NEXTEL 610”(3.9 g/cc), the nominal ply thickness, when fully consolidated, wascalculated to be 0.00692 in (0.176 mm). A piece of prepreg approximately10.1 in (25.7 cm) wide was used to create a 0.375 in (0.95 cm) diameterpushrod.

The prepreg described above was wrapped around a stainless steel tube(0.202 in (0.51 cm) diameter; 0.010 in (0.254 mm) wall thickness;approximately 12-in (30.5 cm) long; available from MicroGroup, Medway,Mass.) such that the fibers are aligned longitudinally along the axis ofthe stainless steel tube. The prepreg was consolidated by wrapping inheat shrink plastic (available under the trade designation “CLYSAR HP”Shrink Wrap Film from DuPont, Wilmington, Del.) and placing it in anoven heated at 100-115° C. for about 30 minutes. The construction iscooled to room temperature (about 23° C.) and the heat shrink plastic isremoved. Alpha-alumina fiber available under the trade designation“NEXTEL 550”, available from 3M Company, was braided around theconstruction using a braiding machine (available from New England ButtCo., Providence, R.I.), yielding an article with a finished diameter of0.380 in (0.976 cm).

The ensuing article was placed in a box furnace (Lindberg Blue M oven,Model 51732-1200° C. available from Lindberg, Watertown, Wis.) andheated at 700° C. for several minutes, thus burning away the epoxy resinand leaving the stainless steel tube and the Nextel fiber preform. Thepreform was placed into a custom-fabricated resin transfer mold aluminumdie (0.375 in (0.95 cm) diameter×14 in (35.6 cm) length cavity) with atop and bottom half split along the centerline of the mold cavities.

Resin Injection:

The preform was placed into the aluminum die set and the entire assemblywas placed in a Wabash hot press (with 15 in (38.1 cm)×15 in (38.1 cm)platen; available from Wabash MPI, Wabash, Ind.) at a clamping force ofabout 10,000 lbs (4,536 kg). On the inlet side of the die set, a metaltube connected the die set with the resin reservoir. The outlet side wasconnected with a metal tube to a vacuum pump (available fromSargent-Welch, Buffalo Grove, Ill.). The resin reservoir was filled withbismaleimide transfer molding resin available under the tradedesignation “651 RESIN” resin transfer molding (RTM) compound fromHexcel Corp., Pleasanton, Calif. Heating tape (available from VWRScientific, West Chester, Pa.) was wrapped around the resin reservoirand attached to a variable voltage power controller to heat the resinreservoir. Concurrently, the top and bottom platens of the hot presswere heated to approximately 315° F. (157° C.). Insulation waspositioned around the exposed sides of the aluminum die set to improveheating efficiency

When the resin viscosity was reduced significantly (temperature above200° F. (93° C.) the vacuum pump was turned on and the exhaust valve wasopened. The vacuum pump thus pulled the air out of the mold and fiberpreform. The inlet valve was opened causing the vacuum to pull theliquid resin from the reservoir into the mold cavity. After about threeminutes, pressure (80 psi; 551.6 kPa) was applied to the inlet side andthe inlet valve was opened. The resin immediately began to flow out theexhaust side of the die set and the exhaust valve was closed. The inletside remained pressurized and the temperature set points on thehot-press platens were increased, raising the temperature to 350° F.(177° C.). The part was cured for 4 hours at 350° F. (177° C.).

Upon cooling, the pressure was released on the die set and the die setwas opened. The finished pushrod was carefully ejected from the moldcavity. The sample pushrod was heated at 475° F. (246° C.) for 16 hours.The ends of the sample pushrod were cut perpendicular to the axis of thepushrod. Annular collars (4130 steel; inner diameter of 0.375 in (0.95cm); outer diameter 0.438 in (1.1 cm); length 0.650 in (1.65 cm)) wereadhesively bonded over the pushrod ends using high temperature epoxy,available under the trade designation “SCOTCHWELD 2214” from 3M Company.Holes were drilled longitudinally into the pushrod at each end to formapertures (approximately 0.220 in (0.558 cm) diameter) and a SmithBrothers endcap (0.3125 in (0.80 cm) ball-end with a 210 degree undercutand a 0.222 in (0.564 cm) diameter shank or pin, available from SmithBrothers Pushrods, Bend, Oreg., was pressed into each end using amechanical, hand operated arbor press (available from Dake, Grand Haven,Mich.). The finished length of the sample pushrod measured from endcapto endcap was 9.450 in (24.0 cm). This preparation yielded a pushrodsimilar to that illustrated in FIG. 1.

Example 2

The epoxy-sized alpha-alumina fiber used in the following preparationswas prepared as follows. A dilute sizing emulsion was prepared bycombining “EPI-REZ 5003-W-55” waterborne epoxy resin (0.6 lb (0.27 kg)),with “EPI-REZ 5520-W-60” waterborne epoxy resin (2.4 lb (1.1 kg); bothepoxy resins available from Resolution Performance Products, Houston,Tex.) and diluting with water (97.0 lb (44.0 kg)) with mechanicalmixing. This dilute emulsion was then applied to alpha-alumina fiberavailable under the trade designation “NEXTEL 610”, from 3M Company,using the following method:

A wound core of alpha-alumina fiber was mounted onto a unwind reel. Thetow of fiber was then dip coated by passing the tow through a bath ofthe dilute sizing emulsion (at about 23° C.). Upon exiting the bath, thewet tow was spirally wound five times around two hot cans (10 in (25.5cm) diameter×14 in (35.6 cm) length at 110° C.-120° C.). The resultingdry, epoxy-sized “NEXTEL 610” fiber coming off of the hot cans was woundup on a cardboard core (0.5% sizing by weight).

As in Example 1 above, the epoxy-sized fiber was converted to prepreg atAldila Inc., Poway, Calif. (88 tows of 10,000 denier fiber were spreadover 12 in (30.5 cm)) to produce a prepreg with a nominal fiber volumeof 63-65% and nominal thickness (at full consolidated density) of 0.005in (0.13 mm). Aldila used a bismaleimide resin to produce the prepreg.The resin was a blend of bismaleimide resin, available under the tradedesignation “MATRIMID 5292A” from Huntsman Advanced Materials AmericasInc., Brewster, N.Y. and co-reactant for bismaleimide resin, availableunder the trade designation “MATRIMID 5292B” also available fromHuntsman Advanced Materials Americas Inc.

Consolidated hollow rods were produced by Aldila using normal state ofthe art techniques. Prepreg was wound around a tapered mandrel(approximately 0.2 in (5 mm) diameter with slight taper) and wound withheat-shrink plastic (available under the trade designation “CLYSAR HP”Shrink Wrap Film from DuPont, Wilmington, Del.). The wrapped articleswere heated (at 350° F. (177° C.) for 2 hours; then 482° F. (250° C.)for 6 hours) causing the tape to shrink and the bismaleimide resin tocure. The resulting 24 polymer composite tubes were slid off the mandreland ground to the desired diameter (half were ground to 0.375 in (0.95cm) and half were ground to 0.438 in (1.1 cm)), each tube being about 18in (45.7 cm) long. Pushrod blanks were cut from these 18 in (45.7 cm)long tubes, using perpendicular cuts.

The tube end portions were further machined to have tapered end portions(0.313 in (0.795 cm) diameter) to accept the annular collars and holeswere drilled into each end (0.228 in (0.580 cm) diameter) to formapertures. The annular collars (outer diameter of 0.375 in (0.952 cm)and inner diameter of 0.313 in (0.795 cm) were pressed on the compositetube ends, followed by pressing in the endcaps (0.3125 in (0.80 cm) with0.230 in (0.584) diameter shanks or pins, available under the tradedesignation “TT3” from Comp Cams, Memphis, Tenn., produced by Trend Inc,Warren, Mich.). The annular collars and the endcaps were additionallysecured by applying high temperature assembly adhesive (available underthe trade designation “LOCTITE 648” from Loctite, Rocky Hill, Conn.).This preparation yielded a pushrod similar to that illustrated in FIG.2.

Example 3

For the preparation of the pushrod of Example 3, the procedure describedin Example 2 was followed with the exception that the composite rod hada starting diameter of 0.4375 in (1.1 cm) and tapers over two inches to0.375 in (0.95 cm) at its ends.

Example 4

For the preparation of the pushrod of Example 4, the procedure describedin Example 2 was followed with the exception that a thin walled (innerdiameter of 0.375 in (0.953 cm) and an outer diameter of 0.438 in (1.113cm)) 4130 steel sleeve (available from Aircraft Spruce, Corona, Calif.)was affixed over the outside surface of substantially the entire lengthof the composite rod (using Loctite 648 high temperature assemblyadhesive (available form Loctite, Rocky Hill, Conn.) after the compositerod end portions were machined, but before the annular collars orendcaps were attached, yielding a pushrod similar to that illustrated inFIG. 4.

Example 5

For the preparation of the pushrod of Example 5, the procedure describedin Example 4 was followed with the exceptions that the end portions ofthe composite rod were not machined, and the steel annular collars werenot applied, yielding a pushrod similar to that illustrated in FIG. 3.

Example 6

For the preparation of the pushrod of Example 6, the procedure describedin Example 2 was followed. Then heat shrink tubing, available under thetrade designation “3M KYNAR TUBING” from 3M Company, was cut to lengthand slid over the pushrod, followed by heating to approximately 175° C.,in order to shrink the tubing snuggly down to the pushrod yielding apushrod similar to that shown in FIG. 5.

Foreseeable modifications and alterations of this invention will beapparent to those skilled in the art without departing from the scopeand spirit of this invention. This invention should not be restricted tothe embodiments that are set forth in this application for illustrativepurposes.

1. A pushrod comprising: a composite rod comprising a thermosettingpolymer matrix and reinforcing fibers within the polymer matrix; asleeve affixed over the outside surface of the composite rod; and anendcap affixed at each end of the composite rod, wherein the fibers areselected from the group consisting of those fibers which comprisepolycrystalline ceramics, boron, silicon carbide, aromatic polyamides,and combinations of such fibers.
 2. The pushrod of claim 1 wherein thecomposite rod is hollow.
 3. The pushrod of claim 1 wherein the compositerod is solid.
 4. The pushrod of claim 1 wherein the fibers aresubstantially continuous.
 5. The pushrod of claim 4 wherein thesubstantially continuous fibers are unidirectionally alignedsubstantially parallel to the central axis of the composite rod.
 6. Thepushrod of claim 1 wherein fibers have a tensile modulus of at leastabout 380 MPa.
 7. The pushrod of claim 1 wherein the sleeve is a metalsleeve.
 8. The pushrod of claim 1 wherein the sleeve is a non-metallicsleeve.
 9. The pushrod of claim 1 wherein the composite rod has acompression strength of at least about 1030 MPa.
 10. A pushrodcomprising: a composite rod having first and second ends and first andsecond end portions comprising a thermosetting polymer matrix andreinforcing fibers within the polymer matrix; an annular collar affixedover each end portion of the composite rod; and an endcap affixed ateach end of the composite rod, wherein each of the collars has a taperedend.